CDK4 and melanoma: Two high-penetrance susceptibility genes, CDKN2A (cyclin-dependent kinase inhibitor 2A, MIM 600160) and CDK4 (cyclin-dependent kinase 4, MIM 123829) and one low-penetrance gene, MC1R (melanocortin-1 receptor, MIM 155555), have been identified so far as genetic risk factors for melanoma [1-3].